With the development of computer technology and applications, the network is widely used in the company and enterprises. For companies, as more and more backups of their important data are backed up on the network, in such cases, it is proposed for the reliability, availability and user of the network at all levels of equipment, especially the center. The higher requirements. In order to enable the availability of the device and high reliability, the server manufacturer, the various components of the product should take the necessary protection, fault tolerance, and the RAID technology, power supply, and fan of the hard disk, all of this. A wide range of applications are obtained in server products. The proposal of these technologies is basically in order to ensure online maintenance while ensuring that the user can operate normally during the system. The hot-plugging or hot swap function is to allow users to take out and replace the damaged hard drives, power or boards, etc. without shutting down the system, and greatly improving the system's disaster. Timely recovery capacity, scalability, and flexibility, so that the fault tolerance of the server system is greatly increased, providing users with maximum availability. Academic statements are: Hot Replacement, Hot Expansion and Hot Upgrade, and hot-swappable first appears in the server field, is proposed to improve server use, in us There are usb interfaces in the computer, which can be hot-swappable. If there is no hot plug, even if the disk corruption does not cause data loss, the user still needs to temporarily turn off the system so that the hard disk can be replaced, and the use of hot-swappable technology as long as it is simple to open the connection switch or turn the handle. Hard disks, and the system can still run normally without interruption. The generation of hot-swappable technology is not open to the server's PCI bus, the peripheral bus is transferred between the CPU, memory and the peripheral device, the earliest microcomputer bus is the PC designed in 1981 in 1981 -Bus is an 8-bit architecture bus, that is, only 8-bit data can be transmitted in a clock cycle.
In 1984, IBM has developed AT-BUS (Advance Technolegy Bus), the number of bus bits reached 16 bits, and the maximum stable transmission rate can reach 5MB / s, but IBM has not announced the specifications of the AT bus, so the AT bus technology controls In IBM, in order to better use this bus technology, the Intel Company, IEEE and EISA Group jointly developed the bus standard specification -ISA bus, namely 8/16-bit "industrial standards" with IBM's AT bus. "Industry Standustry Architecture), the maximum stable transmission rate reached 16MB / s, and then, in 1987, IBM introduced a new bus standard, called MCA (Micro-Channel Architecture) bus, used in IBM On the PS / 2 machine, this bus 32-bit structural bus is greatly improved in transmission rate and stability, IBM is completely incompatible with other manufacturers in order to monopolize this technology. This technology can be used on IBM's PS / 2 machine, and peripheral card using ISA interface technology cannot be used on machines of the MCA bus. If other vendors must purchase IBM if they want to use MCA technology, this makes MCA bus In other vendors, they cannot be promoted, in order to compete with IBM's MCA technology, nine computer manufacturers jointly, according to the nine companies' names Watchzone (Wyse, Ast, Tandy, Compaq, Hewlett-Packard, Zenith Olivetti, NEC and EPSON) organization, based on the ISA bus, "extended industry standard structure" EISA bus designed for 32-bit microcomputer based on the ISA bus, 32-bit address line can be directly addressed in 4GB, 32-bit data Bit, the maximum transmission rate is 33MB / s, and is compatible with the ISA bus. There is also an important technology in the bus technology at the time that VESA LOCAL bus technology, VESA LOCAL BUS is 32-bit local bus, and the VL bus is mainly used on 486, which provides a peripheral device. The communication shortcut between the device and the CPU solves the bottleneck problem of the high-speed device data transmission, but the VL bus is only a temporary, short-term solution, with a lot of limitations, mainly expressing the speed of the VL bus constrained CPU. The VL bus peripheral device card cannot be compatible with the system of each VL bus, the operating frequency of the device card must be the same frequency, and the 50MHz processor needs the terminal device to work in 50MHz, so as the processor The increase in frequency, the peripheral equipment becomes very rare and is very expensive, and only 32-bit bus cannot be extended to 64-bit, which can only fit the 486 machine, whether it is MCA, EISA bus technology, or VESA bus technology, It is accompanied by the current situation of computer technology development and processor, in the 1990s, with the wide application of graphics processing technology and multimedia technology, after entering the PC, after Windows-based graphical user interface, High-speed graphical depiction and processing and high speed I / O processing capability have new requirements, and the peripheral speed has considerable improvement, such as the data transfer rate between the hard disk and the controller has reached 10MB / s. These, the data transfer rate between the graphics controller and the display has reached 70Mb / s.
